Over the last month, the term EVD68 has been making headlines in both the United States and Canada. The acronym refers to a virus, known specifically as Enterovirus species D, serotype 68, although for decades, it has been referred to as EV68 (to avoid confusion with another EVD - the Ebola Virus Disease currently affecting West Africa). At the moment, the virus has been found in 40 States and 4 provinces although its spread is expected to continue.
EV68 may appear to be yet another new and emerging disease but it is well-known by microbiologists. Since 1962, researchers have examined the virus at the biological level to get a better handle on the wide range of symptoms ranging from none to respiratory distress, paralysis and even death. All told, the virus is a rather enigmatic entity with features that are not entirely unique but rather lend from other at times terrifying viral infections.
The enteroviruses are a group of very small viruses (27-30 billionths of a metre in size) and are part of a larger family called the picornaviruses. They were originally classified back in the 1960s without official names, but with numbers. As the discovery of new and emerging viruses continued over the following decades they were reclassified into species with each number being a serotype. Today, there are twelve species with over a hundred serotypes. In the process, one of the greatest threats to our health, poliovirus, suffered a Pluto-like demotion. For those taxonomic sticklers, the virus is now officially called Enterovirus C serotype poliovirus.
Because of the familial relationship of the enteroviruses, many of them possess similar properties in terms of infection. Taking a closer look at EV68, they most closely resemble the rhinoviruses, suggesting they are primarily respiratory agents of disease. Not surprisingly, most infections follow this route with cold-like symptoms and little to no complications. The virus was also expected, much like rhinovirus, to have waves in which the virus would evolve and lead to increased rates of infections in some years.
This evolution happened with EV68 back in Philippines during 2008-2009. The virus had undergone a few mutations and spread rapidly through the country. But, unlike previous incarnations of the virus, there was something different. Many patients suffered from wheezing and/or difficulty breathing. Most survived but two children succumbed to the infection. At the time, this was not considered to be significantly problematic in relation to pneumonia and other respiratory diseases. Still, the cluster suggested the world better be prepared.
Over the coming years, the virus found its way to other countries including Japan, the Netherlands and even the United States. As with the Philippines, the majority of cases were mild with a few hospitalizations and only one death. In all cases, the virus attacked clusters of individuals and did not spread to the general population.
As the virus continued to move quietly around the world, researchers began to take a closer look at the biological functions of pathogenesis to find out why some patients - mainly children - were being so seriously infected. The microscope moved away from the similarities to other enteroviruses and moved to two others known to cause even more serious disease. What was revealed highlighted not only the reason why EV68 infections may be so severe, but also the need to pay closer attention to this virus in the future.
The first revelation came in March of this year. A group of Asian researchers examined just how EV68 enters the cells of the respiratory tract. What they found was surprising. Though the virus appeared to be like the common cold, it actually acted just like the flu virus; in order to infect a cell, EV68 had to bind to the same target, a series of molecules known as α2-6 sialic acids.
The upper respiratory tract is full of these receptors and can easily bind an introduced virus leading to the common cold symptoms. Then, as with the flu, the virus may migrate to the lower respiratory tract and worsen symptoms. For those with pre-existing conditions, such as asthma, infection could lead to significant problems as seen in the 2009 influenza pandemic.
The second finding came in the following month in which a truly global team of scientists discovered what might be an even greater problem. They looked at how EV68 may evade the immune system and prevent certain symptoms, such as fever, from happening. They were shocked to find a mechanism similar to another completely unrelated virus, Hepatitis C Virus (HCV).
The chronic disease caused by HCV is aided by an immune evasion technique whereby chemical signals are degraded before they can alert the immune army to attack. In a similar manner, EV68 uses a protein, known as a 3C protease to break down an immune signal in cells and prevent some of the normal cascades. When this happens, the virus can continue to infect while the person is generally unaware. Then, out of nowhere, severe respiratory symptoms and/or paralysis may occur requiring rapid hospitalization. Both problems may need a long period of convalescence before full recovery.
With these two aspects of the virus now known, public health officials are able to at least ready for the onset of cases and ensure rapid and appropriate treatment is given. However, there are still questions left unanswered. For decades, EV68 has been infecting in clusters. Why now has it changed such that it is so widespread and causing so many more severe infections?
Whatever the reasons for this epidemic, there are a few signs of hope. Like the common cold and flu, infection is entirely preventable by washing the hands with soap and water as well as regularly disinfecting surfaces. Should an infection occur, there is still only a small chance it could get worse; most children and adults will have no symptoms. Finally, if there is a problem, such as respiratory distress, our public health system is prepared and will provide the right care to ensure a speedy and full recovery.
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